Lighting equipment of, for example, automobiles, is composed of molded resin, or lighting bodies, combined with bulbs and lenses. It has been a practice to paint lighting bodies a desired color to match the color of the vehicle body. When the vehicle body is a so-called metallic color, then the lighting bodies are also painted metallic.
FIG. 4(a) shows the sectional view of a conventional metallic coating of a lighting body wherein a plate layer 201 is formed, for example, by an electroplating method, on the surface of a substrate 200 made of a molded resin and a coating film 202 of a desired color is further formed on the surface of the plate layer 201. Since the plate layer 201 is formed as the undercoating layer of the coating film 202, externally irradiated rays permeate through the coating film 202, reflected by the plate layer 201 and then radiate outside through the coating film 202, thus giving a metallic and glossy appearance.
In the conventional coating structure as described above, urethane-based coatings that have relatively high permeability to UV rays (ultraviolet rays) are employed in the coating film 202. Thus, UV rays which irradiate from outside would permeate through the coating film 202 and reach the plate layer 201. As a result of the influence of UV rays, the surface of the plate layer 201 deteriorates and its reflectance lowers.
At the same time, another problem arises. The coating film 202 deteriorates at the interface with the plate layer 201 so that its adhesiveness to the plate layer 201 worsens, thus causing peeling of the coating film 202. To solve this problem, it has been a practice to thicken the coating film 202. However, the thickened coating causes the permeability to lower. As a result, the rays reflected by the plate layer 201 can barely radiate outside and thus the glossiness which gives the desired metallic color cannot be achieved.
Furthermore, when the substrate is provided with sharp-edged projections, as will be described hereinafter, the coating film is typically thinner at these edges. As a result, the above-mentioned peeling of the coating film becomes conspicuous on these edges.
Accordingly, attempts have been made in the conventional art to form a plate layer 301 on a substrate 300 and then form, on the surface of the plate layer 301, a coating film 302 made of a coating containing an UV absorber. Thus, the UV rays reaching the plate layer 301 are reduced by this coating film 302. Although this coating structure is useful in reducing the UV rays that reach the plate layer 301, it is still difficult to satisfactorily solve the problem that a thin coating film 302 peels easily while a thick coating film 302 lessens the glossiness characteristic.